[quote=@1Charak2]
[@Turboshitter]

What is the youngest possible age someone at the Clocktower can have.

[/quote]

The youngest confirmed canon example is Gray at 15, but she's 15 at the start of the story and was recruited as Waver's apprentice earlier than that EDIT: 2 months earlier, actually

[s]I'd guess something like 13 based on that. [/s]